(1) Field of the Invention
The present invention relates to a refrigerating apparatus, and more particularly to technology for controlling the degree of supercooling of liquid refrigerant in a refrigeration cycle.
(2) Description of Related Art
Conventionally, a refrigerating apparatus uses a refrigeration cycle configured by connecting a compressor, a condenser, an expansion valve and an evaporator in this order by refrigerant piping.
In this refrigeration cycle, after low pressure refrigerant that was drawn into the compressor is compressed to a predetermined high pressure, the refrigerant is guided to the condenser and changed into high pressure liquid refrigerant, by the heat exchange with air. This high pressure liquid refrigerant is guided to the expansion valve and expanded, and then sent to the evaporator to be changed to low pressure gas refrigerant, by heat exchange with air to be cooled or with fluid for cooling such as water. Thereafter, the low pressure gas refrigerant is drawn into the compressor and compressed again to repeat the above described refrigeration cycle.
As the condenser in the refrigeration cycle, an air cooled condenser conducting heat exchange between refrigerant and air blown into the condenser is generally used. However, the degree of supercooling of liquid refrigerant that is condensated by this kind of condenser is low at approximately 1° C., and the degree of supercooling may be zero depending on the operating conditions. Therefore, if the liquid-refrigerant does not retain a sufficient degree of supercooling there is a risk of the liquid refrigerant re-evaporating (hereafter, referred to as “flush phenomenon”) due to pressure loss or the like in the liquid refrigerant piping that follows the condenser.
Particularly, HFC refrigerants (for example, R-404A) that are attracting attention in recent years because of environmental concerns are difficult to be supercooled since, in terms of the physical properties of the refrigerants, their volume flow rate is large compared to HCFC refrigerants (for example, R-22). Further, since the circulating volume flow rate of an HFC refrigerant increases compared to, for example, R-22, the volume of refrigerant increases, pressure loss rises, and a flush phenomenon is liable to occur. Examples of problems when a flush phenomenon occurs in liquid refrigerant piping in the refrigeration cycle include a noticeable drop in refrigerating capacity and overfilling of refrigerant when performing an operation to fill refrigerant while viewing the status of flush gas occurrence with a sight glass when performing trial operation for a unit.
Therefore, in order to control this type of flush phenomenon, a refrigerating apparatus has been disclosed that ensures the degree of supercooling of liquid refrigerant reaches a predetermined level by providing a supercooling heat exchanger partway along the liquid refrigerant piping that follows the condenser, and after extracting and decompressing one part of liquid refrigerant from the liquid refrigerant piping on the flow side thereafter, guides the refrigerant to the supercooling heat exchanger to experience heat exchange with high pressure liquid refrigerant (see FIG. 1 of JP-A-2003-279169).
Further, a refrigerating apparatus is known that comprises a plurality of fixed capacity compressors or variable capacity-type inverter compressor and controls the capacity by regulating the number of operating compressors or the driving frequency in accordance with load changes. However, the circulating amount of refrigerant varies greatly when this kind of capacity control is performed. When this kind of control is applied to, for example, the refrigerating apparatus disclosed in JP-A-2003-279169, it becomes necessary to control the degree of supercooling of liquid refrigerant by a supercooling heat exchanger in accordance with variations in the circulating amount of refrigerant. However, no studies have been carried out heretofore regarding this point.
Therefore, for example, when the evaporation temperature of the evaporator is set low or when the circulating amount of refrigerant in the refrigeration cycle becomes low in the case of a small load, an amount of decompressed refrigerant to be evaporated for supercooling is greater than the required amount flows into the supercooling heat exchanger. More specifically, with respect to the high pressure liquid refrigerant and decompressed refrigerant flowing through the supercooling heat exchanger, since the decompressed refrigerant occupies a greater part of the flow ratio, the heat exchange efficiency of the supercooling heat exchanger decreases and evaporation of the decompressed refrigerant in the supercooling heat exchanger is insufficient. Consequently, the degree of suction gas superheating and the degree of discharge gas superheating of the compressor decreases. Further, in the supercooling heat exchanger, there is a risk of a freeze burst occurring due to overcooling, and a refrigerant gas leak or the like being generated as a result thereof.
It is an object of the present invention to provide a refrigerating apparatus that can control the degree of supercooling of liquid refrigerant irrespective of the circulating volume of refrigerant in the refrigeration cycle.